Isomerization of hydrocarbons



United States Patent Oliee Patented Dec. 12, 1961 This invention relates to the catalytic isomerization of light hydrocarbons and is more particularly directed to the production of isomeric C4-C7 hydrocarbons from corresponding normal hydrocarbons and mixtures of the same in the presence of an irradiated catalyst.

In recent years there has been an increasing demand for C4, C5 land C6 isomers, particularly the C4 and C5 isomers. These compounds are particularly useful in upgrading gasollenes to octane ratings that ymeet the continuously increasing requirements of high compression iuternal combustion engines.

Isomerization, both in the liquid and vapor phase, has been obtained by several commercially acceptable methods. One of the early commercial methods utilized metal salts of the Friedel-Crafts type. More recently the vapor phase isomerization of C4 and C5 hydrocarbons has been carried out over a fixed bed of dual function catalysts such as molybdenum on silica-alumina or nickel on silica-alumina. Still more recently an improved isomerization process has been adopted which utilizes a noble metal such as platinum or palladium on a suitable'catalyst base. Both of the foregoing isomerization reactions using either the molybdenum type or the noble metal type have serious shortcomings. For example, the molybdena ycontaining catalysts have high coke forming characteristics and therefore require frequent regeneration. The noble metal type catalysts, while having a low coke forming rate, must be used at comparatively high pressures, in the neighborhood of 900 lbs. per sq. inch, and temperatures in a range of from about 700 F. t-o 1000" F. to provide satisfactory conversion rates. While such processes have been and are being commercially used for the isomerization of light naphthas as well as C., and C5 hydrocarbons, no isomerization process is presently available which will economically convert C6 `and/or C7 hydrocarbons to their respective isomers.

It has now been found quite unexpectedly according to the present invention that substantial yields of isomeric hydrocarbons can be obtained from normal hydrocarbons, including in particular heptane, by utilizing an isomerization catalyst of the platinum or molybdenum type which has been subjected to specic amounts of gamma radiation.

Quite contrary to present techniques high yields of isomerized hydrocarbons, including iso-heptanes, are now obtainable at atmospheric pressure and temperatures considerably lower than the temperatures utilized in existing processes. When isomerization is carriedout under the conditions hereafter described at conventional space velocities with catalysts particularly treated in the manner described, a six fold increase in isomeric product may be obtained. In addition to increasing the product yield, the isomerization process :of the present invention is far more selective than presently available isomerization processes.

lt is therefore an object of the presentinvention to more effectively isomerize hydrocarbons.

It is a further object of the present invention to isomerize normal hydrocarbons overa standard isomerization catalyst which has been subjected to gamma.

radiation.

It is a further object of the present invention to conY vert normal hydrocarbons, in particular-hep'tane to iso-V heptanes, at lower pressures and temperatures than was heretofore possible.

It is .a stil-1 further object 4of the present invention to convert normal heptane to iso-heptane with less cracking and at a higher conversion ratio than it has hereto-fore Ibeen possible by any known isomerizationmethod.

These and other objects and advantages will be more apparent from the description which follows.

FIGURE 1 is a plot of the effect of pre-irradiation of catalyst used in the conversion of n-heptane to isoheptanes.

FIGURE 2 shows a comparison between irradiated and unirpadiated catalysts in a conversion of n-heptane to iso-heptanes.

The present invention viewed in its broadest aspect is directed to a process for isomerizing light hydrocarbons at atmospheric pressure at temperatures in the range of from about 600 F. to 750 F. by means of an isomerization catalyst which has been subjected to suicient gamma radiation to provide the catalyst with a total dosage of at least 1.7 107 roentgens.

While the process of the present invention is generally applicable to the isomerizatio-n of any saturated hydrocarb-on, it is especially suited for the isomerization of n-butane, n-pentane, n-hexane and n-heptane. These hydrocarbons may be used as individual compounds in a relatively pure state. Mixtures such as the butane-butyiene and pentane-amylene fractions from which unsaturated hydrocarbons' have lbeen removed may also be utilized.

ltrier such as alumina or silica-alumina, either with or without an active metal promoter, when exposed to gamma radiation of sufficient intensity and for a period of time suflicient to provide a total dosage of from l.7 l07 to l.3 l08 roentgens an unusually high conversion rate to the isomeric form will result.

The exact reason for this unexpected result is not clear, though it appears that the catalyst is activated to a high energy level which makes it a far more eifectivelisornerization material. Y

The irradiation of the catalyst tothe extent desired may be accomplished in a number of ways. The catalyst:k may be pre-irradiated prior to use in the reaction vessel by subjecting the same to irradiation of suiicient intensity prior to placing the catalyst in the reactor.. If desired, however, the catalyst may be irradiated in situ in the reaction vessel by providing a reaction vessel of such e design that suitable radiation sources may be placed therein to influence the catalyst in place. When such a technique is used, some advantage in convenience of handling results, particularly when regeneration of the catalyst is required. It is to be noted that while the catalyst may `be suitably irradiated in place, the presence of the gamma Y I: cientrtotal dosageY of gamma'radiation in therange set forth will be apparent from FIGURE 1 wherein the percent of conversion of n-heptane to iso-heptane is plotted against the total time of irradiation in hours at a dosage rate of 7 l05 roentgens per hour. This plot resulted from a series of runs on a n-heptane feed at a temperature of 625 F. (125 F.) -which appears to be about the optimum condition for the conversion of maximum amounts of iso-heptane at the total dosage shown. It will be noted that a total dosage amounting to 2.3 108 roentgens produced an adverse effect on the isomer-ization of n-heptane at the 625 F. temperature.

The isomerization may be carried out in either the vapor phase, liquid phase or in a mixed vapor-liquid phase as desired. Normally the lower boiling hydrocarbons are preferably isomerized in the vapor phase, whereas higher boiling hydrocarbons are isomerized in the liquid phase. It has been found that vapor phase isomerization of heptane according to the present methd is most satisfactory. A xed bed of catalyst in a suitable reactor which may be of a tubular or tray design can be used. The catalyst must of course be positioned in such a manner that maximum contact can be made between the feed and catalyst particles. This of course can be accomplished by flowing the feed through the catalyst particles in either a concurrent or countercurrent manner. The presence of a gamma irradiation Ysource in the reaction zone during the isomerization reaction will not adversely aiect either the feed or the prodduct. Y

As has previously been indicated high pressures are generally required for isomerizing the higher normal hydrocarbons such as C6 and C7 when the promoted platinum type isomerization catalyst is used. However, one of the distinct advantages of the present process stems from the fact that the isomerization can be carried out eiectively at atmospheric pressure. In a somewhat similar manner and in contrast to conventional techniques the temperature range suitable for the isomerization is from 600 F. to about 750 F. When a n-heptane feed is being isomerized and a catalyst having a total dosage of radiation in the range specied is being used, a temperature of between about 625 F. and 650 F. is most elective.

Y EXAMPLE In an isomerization reaction carried out according to the method described above, the reaction system containing 100 ml. of platinum on alumina isomerization catalyst having a total dosage of 1.1 108 roentgens was irst purged with nitrogen for approximately 30 minutes, followed by hydrogen gas for 3 hours. Liquid heptane was then pumped into the reaction zone at a rate of 58 ml. per hour together with sufficient hydrogen gas to provide a mole ratio of hydrogen to heptane of 4:1. The temperature of the bed was maintained at 625 F. The product after 40 minutes was collected and discarded, including the product in the cold traps. Heptane and hydrogen were continued through the reaction zone for an additional hour during which time the liquid products from the ice water trap, the Dry-Ice acetone trap and the liquid nitrogen traps were combined and weighed. The exit gas, primarily hydrogen, was measured by means of a wet test meter. The exit gas and liquid isomerate were analyzed by vapor phase chromatography, The exit gas showed traces of methane-and ethane. The liquid sample analyzed as shown in Table I for the run is identied as No. 2.

The importance of the finding that irradiated isomerization catalyst provides a substantial improvement over existing isomerization processes will be more readily apparent from a review of Table I which follows..

4 TABLE 1 Eject of radiation on conversion to heptane isomers Conversion to l-C1 Weight percent Conver- Run Catalyst History sion,

No. Weight percent Selectivlty 1 1 Three Regenera- 'ons. 2 Four Regeneratons, 1.1 X 10El R. 3 Heat soaked-168 hrs. 4 Heat soaked-336 hrs, 1.2 X 108 R.

Fraction converted to i-Gvs X 100 Total Conversion In the foregoing table all runs were made on the same catalyst at 625 F. in the system described in the example. In run No. l the catalyst was not subjected to gamma radiation but had been subjected to three regenerations as indicated. It will be noted that the total conversion of feed which was n-heptane amounted to 12.3% with 34.9% of this value representing iso-heptane. In run No. 2 the catalyst had four regenerations and was subjected to a total dosage of gamma radiation of 1.1 l08 roentgens; total conversion amounted to `32.5% of which 79% represented iso-heptane. The latter represent a 5.9 fold increase in the amount of iso-heptane recovered. In a similar manner another portion of the same catalyst was rst heat soaked for a period of 168 hours as shown for run No. 3 to reduce the cracking tendency of the catalyst. Total conversion using this sample at 625 F. amounted to about 5% with this value representing the total amount of iso-heptane recovered. In run No. 4 the catalyst was further heat soaked and subjected to gamma radiation to provide a total dosage thereon of 1.2 l0 roentgens as shown. Isomerized heptane obtained amounted to 89% by weight of the total 39.9% of the n-heptane converted. As shown in the ratio column at the far right of Table I the irradiated catalyst produced a six fold increase in isomerate.

The substantial improvement, particularly in the isomerization of heptane according to the method utilized herein, is graphically shown in FIGURE 2. In this figure a comparison between an unirradiated and an irradiated catalyst is graphically provided. It will be noted that the irradiated catalyst resulted in a 12.6% conversion to iso-heptane, whereas Ythe unirradiated catalyst at the same temperature produced a 4.3% conversion to iso-heptane.

When isomerization is carried out under the conditions specified, the catalyst treated in the manner described according to the process of the present invention is extremely selective. This will be apparent from Table II wherein analytical data is set forth on a series of runs carried out over a temperature range of from 600 F. to 800 F.

1 Selectlvlty= TABLE II Analytical data on isomerates Total Conver sion Weight percent C i-04 n- G4 1 See definition under Table I. f2 Corrected to 90% overall balance.

In the table the letter R following a temperature indicates that the catalyst was irradiated. It will be noted that excellent selectivity was obtainedV on a n-heptane' feed over the range of from about 600 F. to 650 F.

As in conventional isomerization processes the catalyst of the present invention will after a series of runs require regeneration. The period during which the catalyst may be kept on stream with the regeneration will depend on several factors, including the type of feed, temperature and particular catalyst used. Regeneration may be carried out in situ as accomplished in conventional isomerization processes with air being used to remove undesirable coke laid lown. Since regeneration apparently has no measurable efect on the high level of energyinduced by the gamma radiation it 'will not be necessary to subject the catalyst to an irradiation source during each regeneration, in fact if the catalyst is subjected to the gamma source during isomerization the catalyst may be regenerated may times without being subjected to further dosage to insure maximum electiveness. If the catalyst is pre-irradiated prior to being inserted in the reaction vessel it may be desirable after a series of regenerations to re-irradiate the catalyst by subjecting the same to fur-V ther gamma radiation. This can be accomplished by withdrawing the catalyst from the reaction zone, irradiating the same externally of the reactor and thereafter returning the treated catalyst to the reaction Zone.

While the foregoing process has been described with some particular reference to the isomerization of heptane it is to be understood that the invention is not limited thereto, but may be used for other low molecular weight hydrocarbon feeds in a vapor, mixed or liquid phase process. The particular example cited in which heptane served as the feed is considered to be illustrative of the invention and is not to be construed as limiting the same.

The only limitations to be imposed on this invention are those contained in the claims appended hereto.

We claim:

1. In a process for the isomerization of normal saturated C4-C7 hydrocarbons, the improvement which cornprises contacting a vaporous feed of normal C24-C75 hydrocarbons in a reaction zone, maintained at a temperature of between 60G-700 F., with an isomerization catalyst of the platinum and molybdenum types vwhich has been subjected to suicient gamma radiation to provide the catalyst with a total dosage of from 1.7 10r1 to 1.3 108 roentgens.

2. In a process for the isomerization of an'isomerizable saturated C4-C7 hydrocarbon, the improvement whichV comprises contacting the hydrocarbon in a reaction zone, maintained at a temperature of between 600-750 F., with an isomerization catalyst of the platinum and molybdenum types, said catalyst having been subjected to suicient gamma radiation to maintain a total dosage of from 1.7 X 10I to 1.3 108 roentgens and withdrawing and separating an isomerized product.

3. In a process for isomerizing normal heptane to isoheptane, the improvement which comprises contacting normal vaporous heptane with an isomerization catalyst of the platinum 'and molybdenum type in a reaction zone, maintained at a temperature of about G-750 F., said catalyst having been treated with sufficient gamma radiation to provide the catalyst with a total radiation dosage of from 1.7 l07to 1.3 l08 roentgens, and withdrawing an iso-heptane product. v

4. In a process for the isomerization of an isomerizable saturated CFC, hydrocarbon, the improvement which comprises contacting the hydrocarbon with a noble metal containing isomerization catalyst in a reaction zone maintained at a temperature of from 600-750 F., said catalyst prior to its introduction into the reaction zone having been `treated with sutlicient gamma radiation to provide the catalyst with a total dosage of from 1.7 10'1 to 1.3 108 roentgens, and withdrawing and recovering an isomerized hydrocarbon product.

5. In a process for the isomerization of heptane, the improvement which comprises contacting heptane with a noble metal containing isomerization catalyst in a reaction zone maintained at a temperature of from 60G-750 F., said catalyst having been subjected to sucient gamma radiation to provide the catalyst with a total gamma radiation dosage of from 1.7 l0'I to 1.3)(108 roentgens, withdrawing and recovering an iso-heptane product and periodically regenerating said catalyst.

References Cited in the le of Vthis patent p UNITED sTATEs PATENTS 2,904,483 Long et a1. sept. 15, 1959 2,905,606 Long er a1 sept. 22, `1959 OTHER REFERENCESv Journal of American Chemical Society, vol. 76 (1954), pp. 971-973. f

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIN Patent Nol. 3Ol2953 December 12,1*196I Bertrand W. Greenwald eL al.,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as 'corrected below.

Column 5 line 43 for e1-,Ween 60o-700 F. re d 600-71500 FU Q i k* a between Signed and sealed this 8th day of May 1962.,

SEA L) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIN Patent Nol. 3Ol2953 December 12,1*196I Bertrand W. Greenwald eL al.,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as 'corrected below.

Column 5 line 43 for e1-,Ween 60o-700 F. re d 600-71500 FU Q i k* a between Signed and sealed this 8th day of May 1962.,

SEA L) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents UNITED STATES PATENT oEEICE CERTIFICATE OF CORRECTIN Patent No 3,012,953 December 12, 19,61

Bertrand W. Greenwald et lalt` I It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should reed as 'corrected below Soo7f5 o E, --v

Signed and sealed this 8th day of May 1962o SEAL) Attest:

ERNEST W. SWIDEE Attesting Officer DAVID L. LADD Commissioner of Patents 

1. IN A PROCESS FOR THE ISOMERIZATION OF NORMAL SATURATED C4-C7 HYDROCARBONS, THE IMPROVEMENT WHICH COMPRISES CONTACTING A VAPOROUS FEED OF NORMAL C4-C7 HYDROCARBONS IN A REACTION ZONE, MAINTAINED AT A TEMPERATURE OF BETWEEN 600-700*F., WITH AN ISOMERIZATION CATALYST OF THE PLATINUM AND MOLYBDENUM TYPES WHICH HAS BEEN SUBJECTED TO SUFFICIENT GAMMA RADIATION TO PROVIDE THE CATALYST WITH A TOTAL DOSAGE OF FROM 1.7X10**7 TO 1.3X10**8 ROENTGENS. 